Obviously there is no quick solution here. Approaches to learning vocab vary from person to person , and everybody has their own unique way of learning vocabulary .
Personally I find the easiest way to learn vocabulary is to apply the vocab to real life situations and place the words into context. For example if I was attempting to learn the word "Fahrrad" , I would create a couple of sentences using this word to help it stick in my mind. The association of the word in a context usually helps me to remember it.
At the end of the day , nothing beats repetition and constant reminders of old vocab. Persistence is key !